Hi,I would like to know how could I power my UNO, Ethernet Shield, LCD. The Ethernet use 3.3V and LCD 5V.Can the UNO receive multiple power inputs, thinking dc 5.7V via usb and usb to power adapter and then extra 12V DC from outlet to run the components?How would I achieve this if possible?

"Can the UNO receive multiple power inputs"No. The auto-power switcher will select the voltage at the Vin pin as the current source if Vin/2 >=3.3V.

"thinking dc 5.7V via usb"This 5.7V would not be regulated down to 5V, and you will stand a good chance of damaging the ATmega chips which are not recommended to be powered from more than 5.5V (5V +/-10%)

Aren't the shields designed to either from the 3.3V pin, or take in 5V or Vin and make their own 3.3V or 5V as needed?